Hermetically sealed externally adjustable thermostatic switch



1954 E. J. POITRAS HERMEJTICALLY SEALED EXTERNALLY ADJUSTABLE THERMOSTATIC SWITCH Filed April 5, 1951 fuk uu United States Patent HERMETICALLY SEALED EXTERNALLY ADJUST- ABLE THERMOSTATIC SWITCH Edward J. Poitras, Holliston, Mass.

Application April 5, 1951, Serial No. 219,405

11 Claims. 01. 200-437) My present invention relates to the art of temperature control and regulation and of detection and warning of significant temperature changes. More particularly it concerns thermostatic switches for that field, especially those of the laterally movable strut type as exemplified in United States Patents Nos. 2,090,407, 2,185,433, 2,257,990 and 2,441,725.

The invention aims to render such switch independent of variations in atmospheric pressure including extremes thereof through special provisions whereby the thermally operable parts are hermetically sealed yet the switch may receive setting adjustment externally. At the same time the invention generally improves the structure and arrangement of the thermostatic switch elements with reference to the mounting and housing. thereof, facilitating; assembly and relieving them of casual or superfluous stresses detrimental to maximum efiiciency and sensitivity of operation.

In the drawings illustrating by way of example certain embodiments of the invention:

Fig. l is a longitudinal sectional view of one form of the thermostatic switch; a

Fig. la is a right end view of Fig. 1;

Figs. 2 and 3 are cross-sections of the Fig. 1 device as on the lines 2-2 and 3-3 looking in the direction of the arrows;

Fig. 4 is an end elevation of one end or head member of the Fig. 1 switch, looking at the outer end of said member separately;

Fig. 5 is a longitudinal sectional view similar to Fig. 1' showing another type of switch;

Fig. 6 illustrates in longitudinal section a modified construction for one end portion of the switch; and

Fig. 7 is a cross-section as on the line 7-7 of Fig. 6.

Referring now to Figs. 1 to 4, the thermostatic switch comprises an elongated tubular case, shell or housing 10 formed of a material having a relatively high coefiicient. of expansion, as for example a brass or a stainless steel, the case being of cartridge-like form and preferably seamless construction. Within the shell. 10 there is suspended a switch unit of the laterally movable strut type herein comprising laterally opposed struts 12, 12, of a material of relatively low expansion coeflicient such as a nickel-iron alloy. Associated with the struts 12 are contact points 13 preferably of silver, shown mounted intermediately along the struts.

The switch units may he of a normally open form for making contact on temperature rise to a set point, as in Fig. l, or of a normally closed form for breaking con-- tact with increase of temperature to the set point, as in Fig. 5.

'In the Fig. 1 example the switch selected for illustration is of a single-conductor form for use in a grounded circuit. One of the contact points 13 accordingly is insulated from the corresponding strut 12, as at 14, while the other contact point 1.3 is electrically connected to the strut 12 which carries it. it will be un derstood that any form of the switch, as to making or breaking in response to critical temperature change, may be either of the single-conductor arrangement, such as in Fig. l, or may comprise plural conductors as illustrated in Fig. 5

In the broader aspects the invention is applicable to the laterally movable strut type of switch assembly, whether of the bowed type here shown wherein the struts are ofthe flexible or fiexure hinge type shown, or of a. more rigid type with a theoretical or actual pivotal sup- Patented Dec. 28, 1954 port for one or the other or both struts, as for example in said Patent No. 2,441,725. That is, the invention is useful in connection with any housed strut type of switch wherein a contact-operating longitudinal strut functions in response to longitudinally applied forces resultant from thermal expansion differential as between itself and an embracing case.

Referring again to Fig. l, the contact-operating struts 12 or switch-unit proper are held at the respective ends between header means appropriately spaced lengthwise in the shell 10. Since at one end of the switch unit the header means generally is fixed and at the other is preferably adjustable, the respective ends of the device as a whole may for convenience be identified as the fixed end" and the adjusting end. These happen to be the left and right ends respectively in the drawings and may herein be so referred to for identification, it being understood that such identifying terms have no limiting significance and that the device may be installed and operated in any preferred or convenient position, with the shell axis vertical, horizontal or variously inclined. And with reference to the shell and the external support therefor, such as the mounting flange 39, the parts and elements carried by the shell may be disposed in one orslot in which the fiatwise juxtaposed ends of the struts 12 are entered and secured. The header 20, shown as of substantial thickness, is rigidly fixed in and united with the shell, as by spot welding as indicated at 22. The marginal corner portions of the header 20 are rounded or beveled as at 23 to facilitate assembly into the shell and to afford positioning a channel for an hermetically sealing bondof the header 20 to the shell as by soldering or brazing completely around the circumference.

The single conductor of the Fig. 1 embodiment extends through the header 20 in insulated and sealed relation to it. At this location the conductor comprises a copper or other conductive pin 25 axially embedded in a nonconductive heat-resistant bead-like sleeve 26' of glass or ceramic composition having the reduced inner portion passed through a conformant aperture in the header 20. Such aperture includes an enlarged portion 27 at the outer face of the header to accommodate the insulating bead 26 and an anchor flange 28 fixed on the insulated portion of the pin 25 andseating against the fiat bottom wall of the header recess 27. This flange 28- is circumferentially sealed to the header 20 around the aperture therein as by fusing or brazing thus to complete an hermetic seal at the header 20.

Outwardly beyond the header 20 the shell 10 is closed by an end assembly comprising a hollow tubular pluglike bushing 30 formed of a fibrous, ceramic or other high-temperature electrical insulation such for example as Mycalex. The inner portion of this bushing is of a size to fit snugly in the shell 10 with the inner end abutting the header 20. The outer end of the bushing 30 is somewhat reduced providing an outfacing shoulder 31 over which the end margin of the shell 10 is inturned by a forming action as at 10a. The bushing 30 and the shell 10 may be further intersecured as by circumferential crimping as at 10b.

The axial bore of the insulating bushing 30 includes an inner portion of larger diameter accommodating the beaded conductor pin 25, 26 and the electrical connection thereto comprising lead-out conductor 29 electrically connected to the outer end of the pin 25 as at 29. The outer and smaller bore portion of the bushing 30 defines an infacing shoulder 32 against which is seated a washer 33 receiving the headed-over inner end 34 of a connection post 35. This electrical terminal post 35 is tubular at the inner portion to receive the conductor 29 and to facilitate formation of the anchor flange 34, the conductor preferably being carried axially into or out through the outer portion of the post 35 and being electrically connected and sealed thereto at the outer end to which the appropriate connective lead Wire may be soldered or otherwise attached. To further anchor the terminal post 35 and relieve it of torsional stress a cap flange 36 is applied around the post and welded or otherwise fixed to it. This end flange 36 has one or more longitudinal pins 37 projecting at the inner face and received in anchor holes at the outer end of the bushing 30. The projecting outer end of the post desirably is threaded as at 35a to receive a lock nut 38, a lock washer 38 preferably being interposed between the latter and the cap flange 36. The thermostatic switch as a whole may be variously mounted at the point of use, a mounting flange 39 being indicated in this instance having a collar portion received over and brazed or otherwise fixed to the shell 10.

The electrical connection between the insulated conductor pin 25 is by means of an insulated lead 25a connected at its opposite ends to the inner end of the pin 25 and to the insulated contact point 13. An insulating sleeve 11 of sheet mica or other high-termerature insulation may line the inner Wall of the shell 10 along an intermediate portion of the switch unit.

At the other or adjusting end of the device, at the right in the views, the header means is composite. It comprises a rigid disc or plate 40 having at the inner face a stud 41 in which the fiatwise matched ends of the struts 12 are received and anchored. At the outer face of this strutconneeted member 40 of the header means is a pair of diametrically opposed projections or locating and positioning points 42, 42 shown as protuberances or nubs struck out from the opposit or inner face of the point. Noting particularly Fig. 2 as well as Fig. 1 these locator points 42 are disposed in diametral line an at equal radial distances from the center of the plate, and preferably nearer to the outer margin than to the center so that there is in etfect a substantial radial lever arm between the locator points or positioners 42 and the axis of the plate 40. It is also particularly noted that these positioners 42 are located along a diameter of the plate and of the shell 10 which diameter is perpendicular to the transverse plane containing the ends of the struts 12, that is, the characteristic or central longitudinal plane transversely through the strut unit. The functioning of the parts including the positioners 42 will be further considered. It is to be noted that the header plate 40 is freely received in and is not directly secured to the shell 10.

The composite header means for the adjusting end of the thermostatic switch further comprises an abutment plate 43 having at the outer face a central stud 44. The two plates 40 and 43 constitute an abuttively opposed pair one of the opposed faces of which carries the nodular contact formations or positioners 42, the other opposed face being planar at least in the region of said formatrons.

The outer end of the stud 44 is threaded for reception in an internally or externally threaded sleeve or adjusting screw 45. The latter in turn is centrally threaded into the inner transverse wall-forming por tion of the anchoring and end-closure element 50 cornprised in the header assembly for this adjusting end of the thermostatic switch. Similarly as in the atents mentioned there is a differential in the thread formation as between the internal and external threading of the screw 45, the interior threads here having a higher pitch. Thus turning of the adiusting screw 45 as by means of the tool-engaging slot 46 at the outer end thereof serves to advance the stud 44 and its abutment plate 43 into or to withdraw them outwardly of the shell 10 thereby correspondingly to regulate the set point for the switch unit by increase or decrease of the set compression thereof.

The end closure and anchor element 50 in effect constitutes an extension of the shell 10 and comprises a hollow cylindrical skirt or outer portion 51 of an outer diameter generally conformant to that of the shell 10, and a plug-like inner portion 52 which is solid save for the central threaded aperture receiving the adjusting screw 45. This inner plug portion 52 is reduced an amount equivalent to the wall thickness of the shell 10 so as to have a tight fit in the latter, to which it is afiixed as by spot welding at 53. For further sealing, the joint between the plug element 50 and the shell is channeled and filled as at 54 with a sealing composition such as silver solder or by brazing.

From the foregoing it is apparent that the header means at this adjusting end of the thermostatic switch includes a closure wall which is rigidly secured and sealed to the shell 10 and a pair of contactively opposed disc or header plate members 40, 43 which are variably posionable longitudinally of the shell but are held in selected position of adjustment by the adjusting screw 45 providing an adjustable connection between the stud 44 and the fixed inner end 52 of the end element 50. The stud 44 and its header plate 43 are thus susceptible of regulative movement in the axial direction, but desirably are retained against turning in and relative to the shell.

For the latter purpose and also herein for the dual function of sealing the inner compartment which contains the switch unit, additional hermetic sealing and torsion opposing means is herein provided between the abutment plate 43 and the inner portion of the plug element 50. Such means as shown in Figs. 1 and 5 comprises a metal bellows 55 having the inner end firmly anchored and hermetically sealed to the outer face of A the abutment plate 43 and havingthe outer end similarly attached and sealed to the inner portion 52 of the plug 50, in a circumferential zone surrounding and outwardly spaced from the screw 45, as indicated on the drawing at the respective ends of the bellows.

The bellows 55 is capable of expansion and contraction lengthwise of the shell to afiord the described longitudinal adjustment of the header means for regulating the set point of the switch. But since this metal bellows 55 is of substantial rigidity torsionwise, that is, in a direction to resist circumferential torque, it serves as a means to preserve angular alignment as between the abutment plate 43 and the stationary end element 50 anchored to the shell 10. Thus the header plate 43 and its threaded stud 44 are held against turning in the shell under rotative adjustment of the screw 45.

Means desirably is provided for locking the adjusting screw 45 against unintended turning relative to the fixed end element 50 and hence also relative to the threaded stud 44, the latter being angularly held with respect to the fixed element 50 through the header plate 43 and the bellows element 55 at last above described. Such means herein comprises a lock plate or torque washer seen in section in Fig. 1 and in end elevation in Fig. 3. This lock washer 60 is in the general form of a dished disc formation peripherally recessed to present a plurality of lobes 61 of which four are shown in Fig. 3. The medial dished portion of the washer 60 iscentrally apertured for threaded reception on the adjusting screw 45. The outer margins of the several lobes 61 projecting radially from the apertured hub are disposed in the general plane transverse to the axis of the adjusting screw 45, for abuttive reception against an annular ledge 56 at the inner end .of the skirt portion 51 of the fixed end element 50.

Said end element 50 is shown separately in Fig. 4, looking into the outer end, without the screws 45 and torque washer 60. As there seen the ledge 56 of this end element 50 has one or more notches, seats or locking formations 57, two of which appear in Fig. 4 at diametrically opposite points, adapted to seat in them radially disposed pips or projections 62 spaced 90 apart atthe inner face of the washer 60, one herein on each of the lobes 61. Thus as the washer 60 is turned up against the ledge 56, after rotative adjustment of the screw 45 to the appropriate position, oneor another of the diametrically opposed pairs of pips 62 will snap into said holding seats 57. The other lobes 61 of the washer, which are not then opposite seats 57 of the ledge 56, are in effect stressed outwardly thereby applying an additional biasing stress as between the threaded hub of the washer and the adjusting screw 45, firmly holding the latter against undesired rotation. A special pronged tool adapted to engage in the spaces between lobes of the washer 60 may be provided for turning home the washer into locking position.

Through the means as described the adjusting screw 45 is rendered substantially shake-proof, the axial thrust of the torque washer 60 imposing a strong frictional locking load on the screw 45. At the same time the washer 60 is held against backing out, by reason of the positive angular lock at the outer margin of one radially opposite pair of the lobes 61 and the bumps 62 thereon snapped under tension into the seats 57 'of the fixed end element 50. This same means also functions automatically to signal audibly for a proper degree of axial thrust and loading upon the screw 45. -In operaacesar tact upon the ledge 56' of the end-clement 50. Thereafter it is further turned until a predetermined number of snaps" are heard, cause l by spring seating of an opposed pair of the bumps 63 in the ledge recesses 57, each successive snap being indicative of one-quarter turn of the washer. In an average installation three quarter turns for example are appropriate, as signalled by occurrence of the third successive snap action.

For further protection and discouragement of tampering the end of the device outwardly beyond the adjusting screw preferably is closed, sealed and locked by means requiring a special tool for operation thereof. As shown in Figs. 1 and 1A, such outer closure or sealing cap means is installed in an annular groove 58 undercut at the inner circumferential face of the skirt 51 of the fixed end element 50. An imperforate resilient disc 65 is thrust into the groove 58 and then is locked therein as by means of a spring clip 66 in the form of a split ring having at the adjacent end portions enlargements 67 with tool-receiving apertures 68' for co operation with a plier-like tool having pins engageable in said spaced apertures 68. As a further precaution and to inform of attempts to tamper with the switch, the outer end of" the shell 10 beyond the lock clip 66may be provided with a plurality. of apertures 69 adapted to receive a wire strung transversely across the shell extension or skirt 51 and secured as by a lead seal.

Fig. 5 illustrates an inverse form of thermostatic switch embodying this invention wherein the contacts 113 are normally closed and open upon occurrence of ambient temperature rising to the set point. In this instance the device is shown with plural conductors and corresponding external electrical connections, for use in non-grounded circuits. In this connection it will be understood that the switch types both of Fig. l and of Fig. 5 may be constructed and arranged. either with a single electrical connection and lead in, for use in grounded circuits, or with the dual connections wherein the cir-. cuit is'independent. of ground, as in Fig. 5. In the latter figure the plural struts 112 of the switch unit are bowed inwardly toward each other as for example in Turenne Patent No. 2,257,990, each strut...carrying one of the contact points 113 insulated from it as at 114.

. The anchoring means for the fixed and the adjustable ends of the switch unit and the installation and sup port thereof in the shell are in general similar as in Fig. 1 with the appropriate modification accommodating them to the inverse form of switch unit and to the plurality of electrical conductors 125a. Accordingly at the fixed end the struts 112 are rigidly securedas by welding to a disc header Whichis spot welded to the shell 110 in such transverse position as it naturally as' sumes relative thereto when inserted, similarly as in Fig. 1. The corner edges of the header 120 desirably are rounded as at 123 to assist such conformance. Hermetic sealing at this fixed end of the shell and support for the electrical connections is afforded by a second cross wall 121 seated within a sealing ring 121a itself sealed and spot welded to the shell 110. Conductive pins 125 embedded in non-conductive heat-resistant glass or other ceramic head-like sleeves 126 extend through and are hermetically sealed in apertures through the wall 12.1, similarly as described for the pin 25. of Fig. l. The extrernity of the shell has fitted on it a cup-shaped head 111 providedwith a mounting flange 139 for the device as a whole. External electrical connections are afforded by conductive leads 127 electrically connected at their inner ends to the conductive pins 125 respectively and at the outer ends supported by posts 128 receiving washcr equipped conductor-attaching screws 1280:. The leads 127 and posts 128 are embedded'in an insulating plug 129 seated in the head 111 and further sealing the shell at this end.

At the other or adjustable end of the switch unit and the shell 110 the anchoring and sealing parts may be in general substantially the same as in Fig. 1. Here the abuttively associated header plate pair. comprises an inner plate having a relatively large hub or neck 141 to which the adjacent ends of the struts 112 of the'switch unit are welded or otherwise rigidly secured. The other and outer plate 143 of the pair has at the outer face a stem 144 with threaded outer portion received in the adjusting screw sleeve 145, the latter. in turn threaded in the end closure element 50. vAt the inner face of the outerv plate 143 of the. pair it isitormed with a central post 143:: slidably received in a corresponding'central guide aperture in the opposed inner plate 140. The latterhas at the outer face for contact with the opposed face of the outer plate 143 a pair of nodular formations 142' at diametrically opposite locations. Again as in Fig. 1 these contactive nodes 142 are disposed in a diametral plane (here the plane of the drawing sheet) perpendicw lar to the width of the individual struts 112 and to the central longitudinal plane of the switch unit paralleling said strut width. In said latter plane, here the plane perpendicular to the sheet of the drawings, it will beunderstood that the switch unit is relatively rigid, so that there is little or no opportunity for misaligning deviation thereof in a direction in or paralleling that plane. But in the first mentioned plane, namely the plane perpendicular to the strut width and here coinciding with the plane of the drawing sheet, the switch struts are comparatively flexible and hence under substantial stresses may tend to displacement or distortion in or par-j alleling said plane. By reason of the abuttively related plate pair 140, 143, having inter-contact only at the locations of the nodular formations" 142 in said plane perpendicular to the strut width, the inner plate member 140 rigidly secured to the struts is enabled to conform itself to the outer plate 143 as appropriate for the strut pair 112 and thereby to relieve the-latter of otherwise distortive strain in its said plane of greater flexibility.

Similarly as in Fig. l a tubular metal bellows element 55 surrounds the adjusting stud 144 and is fixed and sealed at its opposite ends respectively to the outer header plate 143 and the end closure element 50. Again as in Fig. 1 the bellows 55 not only affords an hermetic seal with re-* spect to the central threaded parts 144, 145 but also serves as a torsion-resisting connection retaining the longitu-- dinally adjustable header plate 143 in fixed angmlar rela tion to the end closure element 5% and to the shell 110 in which the latter is welded and sealed as at 53, 54. The lock plate or torque washer 60 and removable cover and clip means 65, 66 have Previously been described in connection with Fig. 1, see also Fig. 1A.

In Figs. 6 and 7 a modified construction for the adjustable end of the thermostatic switch is illustrated, such as suitable for installations where full hermetic scaling isof less importance. Here the case or shell 210 is continuous to. the extremity without the skirt-like extension of the end closure element 50 of Figs. 1 and 5. The struts 12 of the switch unit are of the outbowed form of Fig.1 fixed into the central hub 241 of the inner abutment plate 240 which stands in opposed abuttive paired relation to the outer plate 243. The latter has a central threaded stem 244 at the outer face and an axial post 243:: at the inner face slidably received in a central socket 240a in the inner plate 240.

Since in the instance of Figs. 6 and 7 thesealing bel lows element of Figs. 1 and 5 is dispensed with other means is provided for preventing rotation of the header plate 243 relative to the shell 210 and to the end closure element 259 inserted into the shell and welded thereto as at 251. For this purpose the shell 210 is provided, at the inner face with one or more keys 261), two being, shown at Fig. 7 symmetrically disposed at radially opposite positions in the general main plane of the strut members 12. The outer abutment plate 243 is correspondingly formed with peripheral notches 261 slidably spanning the keys 269 and affording axial adjustive movement for the plate 243 but retaining it angularly relative to theshcll 210. The inner plate 240 is notched or marginally reduced to clear the keys in assembling the parts and in the subsequent operation of the switch.

Similarly as in the preceding forms the abuttively associated header plate pair 240, 243 is provided with nodes or locating formations disposed in the central plane perpendicular to the main plane of the switch unit struts which contains or parallels the wide dimension thereof. Also as in the previous forms such contactive projections may be formed on either one of the plates, for..abuttive engagement with the other. In this instance such pro} jections or nodes 242 are carried by the outer piate 243', as best seen in Fig. 7, and present the sole areas of .contact with the opposite outer planar face of the inner plate 240, affording the latter capacity for selfadjusting positional conformity with respect to the outer plate for switch'unit stress relieving purposes as previously ex. plaincd.

" .Qther'. partsat. thisladjusting end'of the shell-pray as in the previous views including the adjusting screw 245, torque washer 263 and cover plate 265. torque washer 263 is shown reversely positioned as compared with the earlier views, being dished outwardly and the axially thrusting portions 262 are disposed about the central aperture of the washer instead of at the outer margin.

From the foregoing description in connection with the drawing it will be evident that the construction throughout and particularly as effects the relation of the two main relatively thermally expansive elements, namely the switch unit and the shell, is made such as to afford maximum avoidance of the setting up of undesired stresses in the switch unit struts. At the fixed end of the latter the header or anchor wall 20 to 120 is self-aligning with respect to the shell. That is, in assembling the parts the switch unit with the wall 20 afiixed is inserted and brought to the approximate location desired axially of the shell and is there permitted to assume its natural conforming position, generally perpendicular to the axis of the shell and with the strut unit extending along the axial line but without necessity for extremely accurate disposition of the wall member 20 or 120 in the shell. These are then welded as at 22 or 122 in the stress-free position naturally assumed. Correspondingly, at the other and adjusting end of the unit a minimum of redundant constraint with respect to the struts is introduced, by reason of the nodular two-point abuttive spacing relation as between the inner plates 40, 146 or 240 and the abuttively associated outer plates 43, 143 or 243 of the respective pairs. As explained, the switch unit itself is substantially rigid in the plane of the strut width, which fact in cooperation with the two-point spacing support provided by the header plate pair in effect cooperates with the latter to give the desirable three-point or three-way support although accomplished with but two actual positioning projections or nodes 42, 142 or 242. Thus at neither end of the switch element are undesired stresses or redundant constraints introduced.

The described construction readily affords opportunity for hermetic sealing as accomplished by the provision of the metallic bellows in Figs. 1 and 5, which element also ideally serves as a torsion lock between the outer header plate of the pair and the shell since it functions both without circumferential lost motion and also without longitudinal friction. Consequently, and especially with the good relative location had with the use of the locating pin such as 143a, 243a, relatively guiding the plate pair, and which locator means may be provided in the Fig. 1 example if desired, together with the described two-point positioning had hythe nodular formations as the points of abuttive contact between the plates, this thermostatic switch returns in remarkable degree to the selected setpoint even after exposure to extremes of over tempera ture. It is further noted that the hermetic sealing which extends the accuracy of the device under high altitude and rarefied atmospheric conditions also contributes to the accurate return capacity for the switch and in general tends for operational efliciency.

v.My invention is not limited to the particular embodiments thereof illustrated and described herein, and I set forth its scope in my following claims:

1. A thermostatic switch, comprising an elongate strutlike switch unit adapted to make and break electrical contact under determined changein longitudinal stress and a tubular containing shell therefor, header means anchoring the opposite ends of the switch unit in and relative to the shell, the header means at one end including a transverse closure wall member connected to the unit and approximately fitting and inserted in self-adjusted across position in and rigidly bonded to the shell, and the header means at the other end comprising a fixed cross wall and a pair of individually integral one-piece inner and outer contact plates, the inner plate fixed to the adjacent end of the switch unit, the outer plate attached to the cross wall, the contact plates having opposing face formations for optimum longitudinal-stress-bearing inter-relation wherein variations from true axial coincidence of the unit and shell under self-positioning assembly of the remote end of the unit are compensated and redundant constraint of the unit is minimized. I

2. A thermostatic switch of the kind comprising a tubular shell and an elongate strut-like switch unit in the shell adapted to make and break electrical contact ..upon determined thermally responsive change in longitudinal stresses between the shell and 'theunit, characterized Such" by transverse header means hermetically closing the shellv variable length surrounding the threaded member and having the outer end sealed with respect to the shell and the inner end sealed with respect to the inner end of the threaded member whereby an hermetically sealed status is maintained for the switch unit while affording said longitudinal stress adjustment therefor.

3. In a thermostatic switch comprising a elongate housing and a contained longitudinal strut-type switch unit, a contactively associated header plate pair at one end of the switch unit, one plate fixed to the switch unit, the other plate longitudinally adjustably securedto the adjacent end of the housing, means holding said other plate against axial turning relative to the shell, each plate having a flat face proximate to and opposing each other, and modular formations at the opposant face of and along a diameter of one plate and engageable with the opposed flat face of the opposite plate for accommodating flexure tendency of the switch unit in a given diametral plane.

4. In a thermostatic switch, a switch unit comprising a pair of laterally opposed struts defining a central longitudinal plane wherein the unit is relatively rigid, a containing shell for the switch unit, headers in the shell for supporting the respective ends of the unit under selective compression, and means for adjusting the compressive setting comprising an outside-inside differential- 1y threaded sleeve threaded axially through one header, a pair of opposed abutment plates, one secured to the adjacent end of the switch unit, the other having a stem threaded into said sleeve and being held against turning relative to the shell, and diametrically aligned nodes on one plate at opposed sides of the axis thereof and abuttively engaging the other plate, said nodes disposed in a plane normal to said longitudinal plane of the switch unit and cotnaining the axis of said stem.

5. In a thermostatic switch, a switch unit comprising a pair of laterally opposed struts defining a central longitudinalplane wherein the unit is relatively rigid, a containing shell for' the switch unit, headers in the shell for supporting the respective ends of the unit under selective compression, and means for adjusting the compressive setting comprising an outside-inside differentially threaded sleeve threaded axially through one header, a pair of opposed abutment plates, one secured to the adjacent end of the switch unit, the other having a stem threaded into said sleeve and being held against turning relative to the shell, abutment projections on one plate along acommon diameter thereof and on opposite sides of the plate axis, said projections abuttively engaging the other plate and disposed in a plane normal to said longitudinal plane of' the switch unit and containing the axis of said stem, and a torsionally resistant metal bellows sealed and anchored to and between the stem-equipped plate and the adjacent header and enclosing said stem.

6. In a thermostatic switch wherein an elongate switch unit is operatively held at opposite ends for thermal actuation in and by a containing shell, the unit having at one end longitudinally adjustable connection with the shell by means comprising a threaded stem, an insideoutside threaded sleeve receiving the stern, and a transverse wall fixed in the shell and having an aperture for the sleeve threaded differentially from the stem, said sleeve extending outwardly beyond the wall, and torsion resisting lock means for the sleeve comprising an annular formation on the wall having angularly spaced seating recesses and a resilient lock plate receivable transversely within the shell and centrally apertured for threaded reception on the extending end of the sleeve and marginally contactible with the annular formation, said plate being marginally recessed to form symmetrically arranged'spaced radial portions,- each such portion having a projection adapted to snap seat into a recessof the annular formation brought opposite thereto under rotation of the plate, non-seated projections reacting with the annular formation to impose axial bias on the plate and' thence to the threaded sleeve, said recesses of the annular formation :being at two diametrally opposite points and the radial portions of the lock plate being in quatrefoil arrangement presenting the projections for audibly signalling snap seating at each quarter turn of the plate.

7. In the manufacture of thermostatic switches Wherein an elongate strut-like switch unit with cross heads at the ends is to be operatively disposed in a tubular containing shell, the method which comprises the steps of inserting the elongate unit in natural unstressed condition to the approximate location desired for it axially within the shell and with the inner head generally perpendicular to the shell axis, securing such head to the shell in the stress-free position there naturally assumed by it, adjustably installing at the opposite end of the unit a supporting abutment element in two-point diametrical eontactive relation to the proximate unit head, and disposing said two-point support in the axial plane which is perpendicular to that paralleling the width of the unit struts, whereby the strut unit is mounted and aligned for reception of longitudinal stress with a minimum introduction of redundant constraint.

8. In a thermostatic switch, an elongate strut-like switch unit carrying contacts adapted to make and break under determined change in axial compression of the unit, a tubular containing shell for the unit, header means fixed in and hermetically bonded to the shell opposite the respective ends of the unit in longitudinal thrust-supporting relation thereto, the header means at one end comprising a fixed cross wall, an inner abutment plate fixed to the adjacent end of the switch unit, an opposing outer abutment plate having a central stem, an adjusting sleeve concentrically receiving the stem and itself concentrically disposed in said fixed cross wall, differential threaded connection between the cross wall and sleeve and between the sleeve and the plate stem, nodular formations on one plate, an opposed flat face on the other plate, said formations located along a diameter of the shell defined by a longitudinal axial plane wherein the switch unit is relatively flexible transversely, the unit having substantial lateral rigidity in the longitudinal axial plane normal to the first-mentioned plane, and a longitudinally expansible tubular element surrounding the inner portion of the adjusting sleeve and the plate stem and fixed and hermetically bonded at the outer and inner ends with respect to the shell and to the stemmed plate respectively thereby hermetically sealing the threaded adjusting connection from the interior of the shell, said expansible-contractible element having also substantial circumferential rigidity adapting it as means to prevent turning of the stemmed plate under adjusting rotation of the sleeve, and lock means to hold the sleeve in adjusted position.

9. In a circuit control device, a housing having an adjusting end, a contained longitudinal bowed strut switch unit, header means at the housing end opposite the adjusting end and having the adjacent end of the switch unit fixed thereto, other header means at the adjusting end of the housing and carrying a longitudinal anchor element, and stress-coupled plates in opposing relation, one on the anchor element and one on the switchunit end adjacent thereto, one plate having a flat circumferentially presented bearing face, the other plate having upon a diameter thereof a counter-acting bearing formation, said circumferential bearing face and said diametral bearing formation standing in disjoined but eontactive bearing engagement operatively interrelating the switch unit and the anchor element for transmission of longitudinal stress one to the other with minimum introduction of constraint for the-switch unit.

10. A circuit control device according to claim 9 wherein the anchor element comprises a stem and a rotatable adjusting member in threaded engagement with each other and with the adjusting member in turn in threaded engagement with the header means which carries it, together with means for holding the anchor element stern against turning under longitudinal adjustment thereof by rotation of the adjusting member relative to the header means.

11. A circuit control device according to claim 10 wherein the means holding the anchor element against turning comprises a torque-resisting bellows surrounding the anchor element and sealed at the opposite ends to the plate of the anchor element stern and to the adjacent header means respectively.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,392,340 Lane Oct. 4, 1921 1,706,523 Churcher Mar. 26, 1929 1,883,046 Spencer Oct. 18, 1932 2,102,098 Sickles et a1. Dec. 14, 1937 2,202,207 Johnson May 28, 1940 2,257,990 Turenne Oct. 7, 1941 2,441,725 Smith May 18, 1948 

